The recipe for global
warming has changed, according to a new statistical analysis of solar output.
A team of scientists says that recent increases in Earths surface temperatures
result not only from greenhouse gases and climate variability, but also from rises
in solar output  a contribution that researchers say climate models have
previously neglected.

The sun, pictured here over Antarctica,
may be increasing its output and contributing to global warming more than previously
thought. Image courtesy of Commander John Bortniak, NOAA Corps.

In 2003, Richard Willson of Columbia University in New York City interpreted more
than two decades of satellite data and concluded that solar output has increased.
Using that data, Nicola Scafetta and Bruce West, researchers in the physics department
at Duke University in Durham, N.C., conducted a statistical analysis to find out
how the increasing solar output affects climate change. The results, published
online Sept. 28 in Geophysical Review Letters, found that from 1980 to
2002, rises in solar output contributed a minimum of 10 to 30 percent to the total
increases in Earths surface temperatures.

The results, Scafetta says, show that solar activity cannot be ignored and that
current climate models need to be changed. The climate seems to respond
to solar changes much more strongly than what present climate models have predicted.

But Willsons solar data reconstruction, from which Scafettas study
is based, is a topic of heated debate among solar physicists. Of the satellites
that monitored solar output since the late 1970s, three consecutive ACRIM experiments
produced some of the most reliable data, which are widely used in solar research.
The Challenger space shuttle disaster in 1986, however, prevented immediate replacement
of the first satellite, leading to a two-year gap, from 1989 to 1991, in the solar
data.

Different methods of bridging the gap, based on data from less accurate satellites,
led to two different interpretations. Although the suns energy fluctuates
naturally within an 11-year cycle, one method shows no change in that cycle over
time, while the other, which Willson and Scafetta used, shows an overall increase.

Judith Lean, a solar physicist at the U.S. Naval Research Laboratory in Washington,
D.C., and colleague Claus Fröhlich dispute Willson and Scafettas claim
of an upward trend in solar output and its purported influence on climate. Lean
says that Willson filled the gap with data from a satellite that did not account
for instrument sensitivity changes over time, which led to his measured jump in
solar output over the two-year gap. He says that this is a secular trend,
but it isnt, Lean says. Its just a jump.

But the debate about the missing data will not end anytime soon. You cant
prove it one way or the other, Lean says.

Measurements of solar output continue via missions such as the NASA-sponsored
Solar Radiation and Climate Experiment, launched in January 2003, which is providing
more data about the suns effect on Earth and climate. Regardless, however,
of whether or not the sun is increasing its solar output, Scafetta says that the
contribution from greenhouse gases alone is sufficient to keep Earth warming.